The task was to find vulnerability in binary service explicit (binary and exploit). Like other tasks at this CTF, this one was easy enouth.
After downloading file and opening it in IDA I'd found that it's x86 ELF which has no imported functions. Unfortunately Hex-Rays FLIRT didn't help me that time, but x86 decompiler works fine and few minutes was enouth to reconstruct main function and identify high level apis. Result I've got is the next: